Fuel cells are electrochemical energy conversion devices considered as a possible alternative to internal combustion engines. Fuel cells convert a hydrogen containing fuel to electrical energy by an oxidation reaction. A by-product of this reaction is water.
One type of fuel cell comprises a solid polymer electrolyte (SPE) membrane, such as a sulfonated fluorinated polymer membrane material known as Nafion, which provides ion exchange between the cathode and anode electrodes. Various configurations of SPE fuel cells as well as methods for their preparation have been described. See e.g. U.S. Pat. No. 4,469,579; U.S. Pat. No. 4,826,554; U.S. Pat. No. 5,211,984; U.S. Pat. No. 5,272,017; U.S. Pat. No. 5,316,871; U.S. Pat. No. 5,399,184; U.S. Pat. No. 5,472,799; U.S. Pat. No. 5,474,857; and U.S. Pat. No. 5,702,755.
The need to provide an appropriate output voltage entails the assembly of many cells, connected in series, into cell stacks. The individual cells are inter-connected by means of a separating interconnection element. The separating interconnection elements also serve the purpose of providing means of transporting reactants and products to and from the cell and thus may be termed as a flow-plate or additionally as a means of managing the heat output of the cell by transfer of heat to the surroundings. Separator plates are manufactured from conducting carbon composites, such as that supplied as SIGRACET Bipolar Plate BMA 5 by SGL Carbon, Meitingen, Federal Republic of Germany and designed and manufactured for use as for one single electrode process.
To obtain high energy densities in Direct Methanol Fuel Cells it is necessary to circulate the methanol fuel to enhance mass transport of reactants to the catalyst by maintaining the lowest possible thickness of the boundary layer. Circulation is generally provided by pumps, which are energy consuming and require maintenance.